pnolans

I'm going to attempt to be as succinct as possible.

I have a 98 XJ Sport with 4.0L engine. Manual transmission.. For the approximately 6 years I've owned it, the oil pressure gauge has pretty much hung right around 40 psi, with no fluctuation while driving.

I recently changed the oil. While doing that , I accidentally broke the Oil Pressure Sending Unit (the cap that the wiring harness connects to).
I replaced it with one from AutoZone. I drove it for about 300 miles on the Interstate. I did not notice any fluctuation at that time.

3 days ago, I started off on a 600 mile trip. I drove about 30 miles (15 on the Interstate). While getting off of the exit ramp, and coming to a stop, I watched the pressure drop to almost zero.
Since I've had that happen before in other trucks and cars, I pulled over immediately and stopped. While parked the PSI came back up, but I was very skittish. I have ignored stuff before and paid dearly for it. Being 67, I have screwed more than one thing up by being lackadaisical. ANYWAY, I chose to not drive back, and had it towed back to my friend's house.

The oil I put in 300/400 miles back is dark. I'm not sure if that's a problem.... I would have expected it to be more clear. When I changed the oil, I put on a Fram filter. After seeing one of those opened up on YouTube videos, I got a K&N filter at Wallyworld, and 5 quarts of Mobile 1. I plan on changing the oil and filter tomorrow morning.

After reading a lot of posts on here, it seems that there is a fair amount of knowledge here.

SO: the question is:

Am I being overly cautious????
....
The OPG needle DOES fluctuate with RPM. It does NOT stay buried at zero. If necessary, I can make and post a video.

Thanks in advance for any help,

Pat

dave1123

My advise is check it with a mechanical gauge. If you have sufficient pressure, then buy a Mopar sensor. There are times like this where factory parts make a difference.

You're going to need another quart of oil. System capacity with the filter is 6 quarts. Chrysler says 15 psi oil pressure at idle is sufficient as long as it increases with additional rpm, but that scares me also. There is a bit of restriction in the banjo bolt that hold the oil filter adapter on, so you can expect a reduction in pressure at idle, but I for one don't like it either. My 2000 4.0 only has 135K miles on it and I'm using Rotella T6 5w-40 synthetic diesel oil. It's holding 25 psi at idle where it's fully hot, but 45 psi at 55 mph. There is a Wix filter that has the right characteristics needed for this engine, but is a lot smaller so I can eliminate the angled adapter but I haven't tried that yet. Finding that filter may be tough. It's a WL7169 and I don't know what vehicle it fits. I found the number on the Wix website. Being smaller, I figure I'll change it between oil changes just to be sure.

pnolans

First, thanks for the detailed reply.
1. I will add another quart before running it.
2. I will look for that Wix filter.
3. I will double check the pressure with a manual gauge.
4. I will post results.

Thanks again,

Pat

dave1123

The thing is, the WJ Grand Cherokees have a different block and because they had to move the motor mounts on the block, there was no room for the oil filter where it was, so they moved it to the main oil gallery on the side of the block and it feeds directly into the lifter gallery. There is no restriction, so no pressure drop. If we can eliminate that adapter, we should get the same result. My 2000 WJ never showed less than 40 psi ever! Even with 253K miles on it! The reason for the adapter is the lack of room next to the frame. The XJ Cherokee was originally designed for the 2.5L 4-banger and they shoehorned the 4.0 into it later. They actually increased the firewall depth to accommodate it. They have cooling problems because there's no room for the air coming thru the radiator to blow past the engine. At least the electric fan blows under the manifolds. There's a auto parts store near me that sells Wix filters, but I haven't had a chance to go talk to him.

If you DO eliminate the adapter, you'll have to pull out the adapter alignment pin and use the filter threaded fitting in the block. All that pin does is keep the weight of the filter from rotating the adapter.

EZEARL

NAPA Gold #1515 is a Wix filter.

When I did the gauge cluster swap years back I cheaped out and bought a non OEM oil pressure sending unit. Didn't last very long.

pnolans

At this point, I think I'm going to assume it's ok. It has not dropped below 1k psi since the day of my "scare". I've been making trips to town (about 20 miles), and it has behaved quite well.

Thanks to all of those who helped. Much appreciated.

Regards,

Pat